This invention is in the field of internal combustion, free-piston, reciprocating engines, and particularly such engines cooperating or combined with linear generators, air compressors or hydraulic pumps for use in a hybrid automobile vehicle, boat, locomotive, or power plant.
Free-piston engines of various types are known and have certain essential features common to them all. The variations of free-piston engines include, for example, a pair of opposed pistons in a single cylinder as seen in U.S. Pat. No. 3,234,395; a central piston rod having end-pistons at opposite ends with a cooperating free-piston axially spaced from each end-piston, thus forming two pairs of free-pistons as seen in U.S. Pat. Nos. 3,541,362; 3,501,087 and 3,347,215; opposed sets of pistons with each set attached to a common rod, the inner pistons of the sets cooperating in a single cylinder and the remote outer pistons of the sets in separate cylinders, as seen in U.S. Pat. No. 4,480,599; and one pair of pistons on a single rod with separate cylinders for each piston as seen in U.S. Pat. No. 4,532,431. The general principles of operation of these and related free-piston engines are well known, with combustion at appropriate times, often by Diesel cycle, providing the power strokes of the pistons combined with appropriate inlet and outlet valves and/or ports.
One particularly significant feature common to all these engines is a compressor component or an inlet for communicating compressed air from an external compressed air source to the combustion chambers. In U.S. Pat. No. 4,532,431, for example, power piston 1 has a backside remote from the ignition plug for compressing air to flow through duct 7 to the combustion chamber. In U.S Pat. No. 3,501,087 piston 19 functions as a compressor; U.S. Pat. No. 3,347,215 discloses a compressor piston and compressed air ducts 19a, 19b, 20a and 20b; in U.S. Pat. No. 234,395 the backside of each piston 18, 19 compresses the air; U.S. Pat. No. 3,370,576 discloses compressed air from an external source for entry via duct 7; U.S. Pat. No. 4,480,599 discloses use of an independent motor 9 or a compressed air system; and U.S. Pat. No. 3,541,362 discloses compressed air from a supercharger or other source, which is a common method for starting free-piston engines of the types discussed above.
As is known, free-piston engines have certain advantages over rotary engines; however, for other reasons, rotary engines have been the subject of vastly greater industrial and commercial success, the most obvious examples being the rotary engines used in automobiles and other land, water and air vehicles. The principal advantage of the free-piston engine is the elimination of the crank shaft; however, the disadvantage as seen in essentially all the prior art free-piston engines is the required air compressor component or connection to a source of compressed air.
A conventional prior art free-piston engine is shown schematically in FIG. 2 of the drawings herein where the inner sides of the two pistons 4 operate within the cylinder as compressors, thus necessitating additional space and weight. A feature of free-piston engines which have opposed pistons is apparatus to balance and coordinate these pistons. One arrangement is to provide a pinion whose axis of rotation is perpendicular to the longitudinal axis of the free-pistons and cylinder. The pinion is engaged on one side by a rack extending from the left piston and is engaged on the other side by a rack extending from the right piston. Thus, as the pistons move toward each other in the cylinder, the pinion rotates in one direction, and when the pistons move away from each other the pinion rotates in the reverse direction; however, at all times the axial displacement of one piston is controlled to have exactly the same magnitude and opposite direction of the other piston.
Because rotary engines with crankshafts are so common the nomenclature describing their operation has become essentially standard, even in part for use with free-piston engines having no rotary crankshafts. For example, a free-piston is described as being at top dead position (TDP), or at lower dead position (LDP), or at 30 degrees of crank rotation before LDP, even in the absence of any rotary crank. More specifically in a free-piston engine, the two opposite extreme linear displacements are called LDP and TDP for lower dead position and top dead position respectively, and the intermediate piston linear displacements are treated as if they are fractions of the 180.degree. rotary crank displacement between these dead positions.
In the history of rotary engine development one concept that was discovered about fifty years ago but not utilized commercially was an air pressure phenomenon called the "Kadenacy effect", named after its discoverer. Kadenacy modified a two-cycle, rotary, Junker Diesel engine by eliminating a compressor or blower attachment for the inlet air and altered the timing of the inlet and outlet ports which led to substantially increased rotary speed and horsepower. Two curious aspects of this alteration were lower inlet air temperature, by eliminating heating resulting from compression, that led to increased volumetric efficiency and an actual negative pressure in the bottom part of the air admission and exhaust region that aided in admitting fresh air into the cylinder without aid of an air compressor.
To commercialize free-piston engines has been an unfulfilled dream of engine makers for many years, the main problem being the costly and bulky air compressors required since there was no crankshaft to drive the piston in a compression stroke. The above-mentioned "Kadenacy effect" was not applied to free-piston engines, firstly, because it was originated for rotary engines with no contemplation for use in free-piston engines, secondly, no one even considered eliminating the compressors always deemed necessary in free-piston engines, and thirdly, because the "Kadenacy effect" was not even accepted and used commercially in the world standard rotary engines and therefore not imaginable for free-piston engines.
Extensive disclosure of the Kadenacy concepts may be found in the U.S. patents of Kadenacy, Nos.
______________________________________ 2,102,559 2,123,569 2,131,959 2,147,200 2,110,986 2,131,957 2,134,920 2,167,303 2,113,480 2,130,721 2,144,065 2,168,528 ______________________________________
Kadenacy's claims were acknowledged by some experts in the field and ignored and even ridiculed by others, as is discussed in the article "Taking the Mystery Out of the Kadenacy System of Scavenging Diesel Engines" by P. H. Schweitzer, C. W. Van Overbike, and L. Manson in the October, 1946 "Transactions of the A.S.M.E.", a copy of which is appended hereto as Appendix III.
In summary, the Kadenacy theories have been either acknowledged by some or challenged by others, but generally not accepted or followed, and certainly not considered by person's skilled in the art as an acceptable or workable system for use or combination into a commercially feasible engine.
The free-piston engine of the present invention has particular application in combination with a linear generator for powering a hybrid automobile or for other purposes. The subject of hybrid vehicles has lured professional and amateur scientists to spend vast amounts of time and money, thus far without commercial success even though there has been much progress with the storage battery elements and motors used in the all electric vehicles. Reports of these developments may be found, for example in the book Electric and Hybrid Vehicles by M. J. Collie, 1979, Noyes Data Corp., Park Ridge, N.J., portions of which are annexed hereto as Appendix I and in the article "Gasoline/Electric Sports Car" by Dan McCosh, pp. 76-79 in Popular Science, August, 1986, a copy of which is attached hereto as Appendix II, the full texts of these appendices being incorporated by reference herein. In Electric and Hybrid Vehicles on pages 25-31 and pages 193-203 there is discussion of electric and hybrid vehicle systems, operating modes and components, with a particular survey of prior art combustion engine power sources, namely "reciprocating" spark-ignition engines, diesel engines, rotary engines, Stirling engines and gas turbine engines. It is noteworthy in this reference that the free-piston engine is not even mentioned or considered as the heat or combustion engine component for hybrid vehicles. In the Popular Science article of Appendix II the author, illustrating a typical reciprocating V or in-line combustion engine, states,
Since the beginning of the automobile age, power has been transferred from engine to wheels through drive shafts and transmissions. The goal with the new system is to break with that tradition entirely and convert the raw energy of an internal combustion engine--still the lightest, most efficient source of on-board power for a car--into electricity that powers a motor at each wheel.
Additionally, the separation of the engine shaft from the wheels of a vehicle permits the engine to run at its maximum efficiency and results in a 100% increase in efficiency. When the battery of a hybrid vehicle is completely charged, the engine stops by itself; when the battery's charge is low, the engine runs, thereby charging the battery with its highest efficiency. Thus, such a hybrid vehicle is twice as efficient as conventional ones, and such a hybrid passenger automobile is able to get 100 miles to the gallon.
Obviously, with this intense concern to improve power versus weight and efficiency relative to power and weight, an improvement of these parameters in the engine would be equally or more significant than the improvements in the electrical components, i.e. the generators, generator-motors, fly wheel-generator-motors, batteries, and electronic logic and control systems many of which have already been improved considerably to their current status. The present invention provides such an improved combustion engine power source in a new free-piston engine.